1. Field of the invention.
This invention relates to a novel process for preparing stable, non-aqueous solvent solutions of acid-functional polymers which are prepared by the reaction of cyclic carboxylic anhydrides with hydroxy-functional polymers. Acid-functional polymers prepared by the half-ester reaction of the hydroxyl groups of hydroxy-functional polymers with cyclic carboxylic anhydrides as taught herein are useful as co-reactants in a number of applications, such as chain extension or crosslinking of polyepoxides, polyamines, or polyhydroxy compounds.
2. Description of the Prior Art.
The reaction of cyclic carboxylic anhydrides, such as maleic anhydride, with hydroxy-functional molecules to produce a half-ester having an ester group and a carboxylic acid group has been known in the art. However, these acid-functional materials frequently do not remain stable for long periods of time and often demonstrate increased viscosity and even gellation upon storage. The novel process of this invention greatly minimizes the instability on storage and corresponding viscosity increase of these acid-functional materials by conducting the half-ester reaction of the anhydride and the hydroxy-functional molecule at temperatures less than about 75.degree. C. until the reaction of the anhydride and the hydroxyl groups to form the half-ester has been completed to the desired extent and, thereafter, adding to that reaction product a stabilizing amount of a low molecular weight alcohol solvent.